When dealing with broken bone fragments of small size, such as those of the phalanges or the toes, the small size of the bones or bone fragments concerned poses difficult problems to be solved by the practitioner in charge of reducing the fracture and then putting the bones into place with sufficient compression to ensure that the fracture is properly resorbed.
In order to ensure rapid osteosynthesis between two bone fragments, leading specifically to the rapid formation of a high quality bone callus enabling a rapid return to normal function, it is necessary for two small bone fragments to be positioned and fixed relative to each other with relative longitudinal compression being established between the two bone fragments.
Clearly, given the very small size of the bone fragments concerned, and the correspondingly small size of the osteosynthesis screws used, it is difficult to establish longitudinal compression between the two bone fragments concerned.
It is particularly important and difficult to master this type of surgical act, given that the manipulations imposed by the small size of the bones and the screws are fiddly, and given that the small bone fragments need to be positioned relative to one another and compressed and put into final position with very great precision since the purpose is to restore total mobility functions, such as handling functions or walking, in particular when dealing with bones of the hand or of the foot.
It is thus already known to use staples that are put into place directly on the two bone fragments to be joined together. Such a technique is poorly adapted to the type of surgery under consideration insofar as putting staples into place relative to the pieces of bone does not make it certain that the bone fragments to be joined together are properly positioned. In practice, it is not possible with staples to obtain fixing and compression.
Proposals have already been made to use osteosynthesis screws of the kind used for coaptation of bones of large size and suitable not only for joining bones together, but also for performing the additional function of applying longitudinal compression.
Thus, proposals have already been made to use an osteosynthesis and compression screw comprising a proximal portion formed by a screw head provided with an outside thread and presenting a diameter greater than that of the remainder of the screw. The screw presents an intermediate portion without any thread in order to improve relative sliding between the bone fragments for joining together while the screw is being screwed in, and said intermediate portion is followed by a distal portion which is also provided with an outside thread.
Such screws improve surgical operating conditions greatly because of the improve ease with which they can be put into place.
Nevertheless, such screws still suffer from drawbacks associated in particular with a certain number of additional actions that the surgeon needs to perform such as prior drilling of a hole in order to ensure that the threads of the screw hold strongly both in the distal portion and in the proximal portion having the head of larger diameter. This increases the number of actions the surgeon needs to perform and therefore increases the duration of the operation.
Considerable improvements have been provided to screws of this type but they relate essentially to increasing the compression ability of such screws, for example by incorporating a two-start distal thread, without taking account of total time required for surgery but while maintaining excellent holding strength and compression properties.
Conventional self-boring and self-tapping surgical screws are also known, with the tapping portion of such a prior screw nevertheless being restricted to the distal portion thereof. Screws known in the prior art possess a screw head that is not threaded and that must specifically be embedded in the bone by previously making a suitable recess using a special tool. Such screws thus require an additional tool to be used which implies an additional act leading to increased manipulation, to additional risk of accidents or faulty installation, and, in all, lengthening the time required for surgery.